It is known that the belt drive of an internal combustion engine serves for the drive of auxiliary assemblies of the motor vehicle, such as, for example, the generator, air conditioning compressor or water pump, and is designed, as a rule, as a belt drive driven by the crankshaft of the internal combustion engine. Since the individual auxiliary assemblies, as a consequence of their functions, are arranged offset with respect to one another on the internal combustion engine, the belt drive is provided with deflector pulleys for the belt which deflector pulleys are fastened rotatably to the internal combustion engine and which in each case ensure a sufficient looping around of the belt pulleys of the auxiliary assemblies. At the same time, the required tension of the belt is set with the aid of a tensioning pulley which is likewise fastened rotatably to the internal combustion engine at a pivoting arm acted upon by a spring force. Tensioning or deflector pulleys of this type consist essentially of a plastic or steel running roller which is formed essentially by an inner hub ring and an outer running ring and by a wheel disk connecting the two rings to one another, and of a radial rolling bearing which is fixed in position in the hub ring of the running roller and which consists of an inner bearing ring and an outer bearing ring and of a multiplicity of rolling bodies which roll between the bearing rings in groove-shaped raceways and which are held at uniform distances from one another by a bearing cage. Furthermore, the radial rolling bearing has axially on both sides of its rolling bodies one seal each by means of which the interspace between the bearing rings, which is designed as a grease repository, is sealed off.
Such a tensioning or deflector pulley is already known as generic, for example, from DE 100 61 995 A1. In the running roller disclosed in this publication, the radial rolling bearing is designed in the usual way as a single-row grooved ball bearing which is cast with its outer bearing ring into the hub ring of the running roller consisting of plastic. The rolling bodies of this grooved ball bearing in this case consist of a defined number of bearing balls which roll in groove-shaped raceways in the inner and in the outer bearing ring and which are held at uniform distances from one another by means of a bearing cage. The interspace between the bearing rings which is designed as a grease repository is sealed off by means of what is known as a two-stage seal, the first stage of which consists in each case of a reinforced lip seal and the second stage of which is formed in each case by a further sealing disk axially preceding the first stage with an annular sealing gap.
The lip seals are thus in each case fixed in position in an annular slot at the outermost margin in the inside of the outer bearing ring and, brushing via an elastic sealing lip, are supported in each case in a peripheral slot at the outermost margin in the outside of the inner bearing ring of the radial rolling bearing. By contrast, the further sealing disk is designed as a separate annular metal disk which is plugged with its inside diameter on a head-side centering extension of the fastening screw of the running roller and which is braced between the inner bearing ring and the screw head of the fastening screw. At the same time, the sealing disk extends radially over the entire height of the interspace between the bearing rings of the radial rolling bearing and on its outer circumference has an elastic sealing lip which is supported on the axial end face of the outer bearing ring.
The disadvantage of this known tensioning pulley, however, is that the grooved ball bearing used for its mounting, particularly on high-performance and high-torque internal combustion engines, comes up against the limits of its load-bearing capacity more and more often due to the high operating forces and is consequently subjected to increased wear, because of which the grooved ball bearing has to be exchanged prematurely. The cause of the limited load-bearing capacity of such a grooved ball bearing is in this case to be seen in the limited number of mountable bearing balls which, in such bearings, are introduced by what is known as the eccentric mounting method, in which the two bearing rings are arranged eccentrically to one another, the free space thereby occurring between the bearing rings is filled with the bearing balls, and, thereafter, the inner bearing ring is brought into the position concentric to the outer bearing ring, utilizing the elasticity of the two bearing rings. Finally, the bearing balls are distributed uniformly in the raceways of the bearing rings, and the bearing cage is inserted, and therefore it is, as a matter of course, impossible to fill the bearing fully with bearing balls by means of this mounting method.
Even the obvious possibility of increasing the load-bearing capacity of the tensioning or deflector pulley using two-row grooved ball bearings is limited, mostly because of construction space, at least in passenger vehicles, and therefore two-row grooved ball bearings are employed preferably for the tensioning and deflector pulleys of the belt drive of commercial vehicles, but, even in these, often come up against the limits of their load-bearing capacity because of increasingly higher-performance internal combustion engines.
It is also a disadvantage, in the grooved ball bearing used in the known tensioning pulley, that its available grease repository for lubricating the bearing has a relatively small design. Since, as a consequence of construction, no relubrication possibilities are provided for the radial rolling bearings of tensioning and deflector pulleys, the useful life of the grooved ball bearing is therefore also dependent on the size or possible period of use of the existing grease repository. The size of the grease repository is in this case defined by the free volume of the interspace between the bearing rings which, in the grooved ball bearing used, is reduced considerably due to the volume of the bearing balls and of the bearing cage and, at least in grooved ball bearings with standard dimensions, also cannot be extended without major expenditure.
Finally, even the two-stage sealing of the grooved ball bearing of the known tensioning pulley has proved to be a disadvantage in that the further sealing disks preceding the inner lip seals are designed as separate individual parts which are delivered together with the tensioning pulley and constitute the intended functional unit with the lip seals only when the tensioning pulley is being screwed to the internal combustion engine by the final manufacturer. However, such designs in a differential type of construction no longer conform to the present-day requirements of the automotive industry in terms of system solutions from the supply industry, whereby, in this particular case, the tensioning pulley is designed as an integral component with all seals, which merely has to be finally mounted as a functioning module on the internal combustion engine.